# Tennis physics: when does a served ball stop accelerating?

**URL:** <https://boards.straightdope.com/t/tennis-physics-when-does-a-served-ball-stop-accelerating/544813>\
**Category:** Factual Questions\
**Created:** [June 28, 2010, 5:36pm UTC](https://boards.straightdope.com/t/tennis-physics-when-does-a-served-ball-stop-accelerating/544813 "2010-06-28T17:36:23Z")\
**Posts on this page:** 4\
**Page:** 2

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**Author:** ![DanBlather](https://avatars.discourse-cdn.com/v4/letter/d/f4b2a3/32.png) [@DanBlather](https://boards.straightdope.com/u/DanBlather)\
**Post date:** [June 29, 2010, 2:04am UTC](https://boards.straightdope.com/t/tennis-physics-when-does-a-served-ball-stop-accelerating/544813/21 "2010-06-29T02:04:50Z")

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Y’all are ignoring any curvature in the flightpath from the spin of the ball and the effect of the difference in air speed on opposite sides of the ball. As has been noted, acceleration is a change in speed or direction.

So to summarize for the OP who is now probably totally confused: the tennis ball will begin to slow down as soon as it loses contact with the racket, but there will be some second order effects due to air resistance and gravity accelerating the ball downward.

The same is true of bullets and cannon balls.

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**Author:** ![yoyodyne](https://avatars.discourse-cdn.com/v4/letter/y/a9a28c/32.png) [@yoyodyne](https://boards.straightdope.com/u/yoyodyne)\
**Post date:** [June 29, 2010, 4:19am UTC](https://boards.straightdope.com/t/tennis-physics-when-does-a-served-ball-stop-accelerating/544813/22 "2010-06-29T04:19:03Z")

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> [@lisiate](#):
>
> Wikipedia’s article on the [Magnus effect](http://en.wikipedia.org/wiki/Magnus_effect) shows what’s going on with the ball’s spin. The force imparted by the spin operates perpendicular to the ball’s motion through the air (either side to side or up and down but not forward or back). So any spin doesn’t result in any acceleration towards the receiver.

True, but it does cause acceleration after the ball has left the racquet, and that in turn increases or decreases the distance the ball travels. In keeping with the spirit of the OP, if not the letter 😉

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**Author:** ![Bryan\_Ekers](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/bryan_ekers/32/183_2.png) [@Bryan\_Ekers](https://boards.straightdope.com/u/Bryan_Ekers)\
**Post date:** [June 29, 2010, 5:07am UTC](https://boards.straightdope.com/t/tennis-physics-when-does-a-served-ball-stop-accelerating/544813/23 "2010-06-29T05:07:45Z")

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> [@Telemark](#):
>
> After the ball leaves the racket what could be acting on the ball to accelerate it?

The sonic pressure of the player’s grunt. Monica Seles could get an extra 5 mph.

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**Author:** ![brossa](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/brossa/32/3040_2.png) [@brossa](https://boards.straightdope.com/u/brossa)\
**Post date:** [June 29, 2010, 10:32pm UTC](https://boards.straightdope.com/t/tennis-physics-when-does-a-served-ball-stop-accelerating/544813/24 "2010-06-29T22:32:39Z")

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Being smashed by the racquet and then rebounding to a more-or-less spherical shape would cause the tennis ball to ‘ring’ after it leaves the racquet surface. This ‘ringing’ would not affect the velocity of the center of mass of the ball, but the velocity of a point on the leading edge of the ball would oscillate around that mean value. So, if you were just measuring the velocity of the leading edge of the ball, it would probably continue to accelerate for a fraction of a second after leaving the racquet surface - then it would appear to slow down, then speed up again, etc. until hysteresis damps out the ball’s oscillation.

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